This invention generally relates to liquid polyester resins with surface treated fillers. Further, this invention relates to the use of the surface treated fillers in liquid polyester resins to provide improved thixotropic properties.
The use of fillers in plastic fabrication to enhance physical properties as well as reduce costs is well known in the art. However, when fillers are used in large amounts to increase the viscosity of a plastic the filler can have an adverse affect on the physical properties of the plastic. It has therefore become desirable to control viscosity by other means.
Viscosity control is an important part of many plastic fabrication processes. Many manufacturers add a thixotropic agent to cause the liquid resin formulation to have a higher viscosity at high shear rates than at low shear rates, (i.e., thixotropic properties). Thixotropic resin formulations have utility in a variety of applications, particularly, in coatings, spray-up applications, impregnation of fiber mats, and gel coats where low shear viscosities allow ease of application and higher unsheared viscosities prevent dripping, sagging and running once the resin has been applied. The anti-sag, anti-run properties are particularly desirable for applications involving vertical surfaces where sagging and running are significant problems.
A typical (but expensive) thixotropic agent is fumed silica. Generally, the thixotrope is added in addition to other fillers and additives in resin formulations. Fillers, such as, calcium carbonate or alumina trihyrate are commonly used in liquid resin formulations to reduce cost, increase stiffness or impart other desirable properties such as fire retardance but often these fillers do not impart thixotropic properties to the resin formulation. Accordingly, it would be desirable to modify these fillers with a surface treatment such that these fillers would impart to the resin formulation thixotropic properties without the need of additional thixotropic agents.